This invention relates to methods and systems for performing attitude control of a tunneling machine shield and, more particularly, to improvements in the attitude control method of the tunneling machine shield for accurately excavating tunnels through ground layers in an intended excavating direction and in the system for performing the method.
In tunnel excavations employing the tunneling machine shield, a cylindrical shield made of a steel is advanced by means of many propelling jacks substantially peripherally abutting against a rear end of the shield so that the shield will be urged against the ground toward which a forward head part of the shield is facing. An excavated tunnel wall surface exposed right behind the shield consequent to such advance of the shield is retained by a retaining wall member or segments installed so as to overlap internally the rear end of the shield, by repetition of which steps a tunnel is made in the ground.
In such shield tunnel excavations of the kind referred to, it has been required to maintain the shield accurately in axial alignment with the intended excavating direction of the tunnel during the propulsion of the shield so as not to cause any positional deviation from the direction. In order to achieve this purpose, such light beam irradiation means as a laser or the like is installed in the tunnel already excavated behind the shield. A positional deviation detecting means for receiving a light beam from the light irradiation means and detecting any deviated amount of an actually received position of the beam from the central "zero" position of the detecting means is provided in the shield and includes a gyroscope. In the case when there occurs a certain amount of the positional deviation from the intended excavating direction, the detecting means or the gyroscope detects the deviated amount and generates a positional output signal corresponding to the amount, which signal is provided to an attitude controlling means for the shield. In the controlling means, the positional output signal is processed in a manner known per se and a deviated direction and deviated amount are indicated through a servomechanism. In accordance with thus indicated deviated direction and amount, the propelling jacks for the shield are selectively driven so as to correct such direction and amount and thereby the attitude of the shield is corrected.
In this case, it is desirable that the attitude control operation is performed within a short period and in a simple manner since, unless the shield's attitude control is rapidly established, the deviated amount is to be increased and consequently a weaving distance of the shield propelled is caused to be larger. Further, it has been found that a proper propulsion force given to the shield depending on the nature of ground formations would result in an effective attitude control.